hostmot2 changes: Config changes required! pwmgen.scale now works as advertised; stepgen timing params are "u32 ns" instead of "float seconds"; and stepgens now have a .enable pin which needs setting.

hostmot2 feature additions: Added PDM mode for pwmgen; PWM and PDM frequency are now settable by the user; implemented stepgen maxaccel and maxvel; support open-drain GPIOs; all GPIOs now have some representation in HAL (though the ones used by module instances are restricted); encoder improvements.

Lots of hostmot2 bug fixes, mostly with pwmgen and stepgen. Thanks to all the brave testers!